Fluid Simulation falls under the category of gesture-based simulation apps and it is one of the best which I have come across lately. The app opens up as a pitch-black screen on which you can tap, swipe, or twirl your finger(s) to create mesmerising fluid animations. The app supports multi-touch gestures.
You can even manipulate many of the factors to make your custom fluid animation and save it as a preset for using it later. Moreover, the animations are so cool and crisp that after creating a pattern, you can quickly screenshot it to make it your wallpaper of the day.
Download Fluid Animation on Android and iOS (Free, one-time payment of $2.69)